1. Field of the Invention
The present invention relates to a power supply device for an electronic equipment suitable for use with a video camera recorder, for example. More particularly, this invention relates to a power supply device for electronic equipment in which an operation alarm voltage and an operation end voltage can be accurately identified even when characteristics of an external battery connected to electronic equipment through a connecting means are changed.
2. Description of the Related Art
Video camera recorders, for example, use a rechargeable external battery pack as a power supply thereof. In that case, the main body side of electronic equipment detects from the battery power supply the situation in which the external battery pack is consumed and displays on an arbitrary display means an alert message for letting users know when the battery pack will be fully consumed soon and an operation end message in which the battery pack is fully consumed and the electronic equipment is made unable to operate.
Specifically, in such apparatus, for example, the electronic equipment body side measures a terminal voltage of a power supply terminal of a battery connecting means. In these electronic equipments, there are previously set threshold values for operation alert message to let users know when the electronic equipment body will not be operated normally soon and threshold values for operation end message for letting users know that the electronic equipment is no longer operated normally. Then, the operation alert message and the operation end message are displayed by comparing the above-mentioned measured voltage values and these threshold values.
Recently, a variety of dry cells are commercially available on the market as an external battery. Depending on the kinds of the dry cells, it is frequently observed that some dry cells demonstrate battery characteristics different from those previously expected. That is, although it is customary that the above-mentioned threshold value for the operation alert message is set with a voltage difference in such a manner as to have a predetermined operation time prior to a threshold value of an operation end, if a voltage changing ratio during such period of time is changed, then relationships between a voltage difference and a time will not agree with each other.
In other words, in a dry cell having a characteristic in which a voltage, for example, is lowered progressively and a dry cell having a characteristic in which a voltage that has been kept to a certain degree is lowered rapidly, not only the settings of the operation alert message threshold value but also the settings of the operation end message threshold value become different from each other. However, a conventional electronic equipment in which a terminal voltage is measured by only the main body side is unable to cope with the change of the characteristics of the dry cell.
Therefore, according to the conventional apparatus, when a battery with a dry cell having different characteristics is connected to an electronic equipment, there is then the risk that the operation alert before the battery consumption and the operation end display for displaying the disabled state caused by the battery consumption will not be made correctly.